Praserthdam, Supareak (2018-08). Computational Study of Reactive and Coke-Resistant Catalysts for the Dry Reforming Reaction of Methane. Doctoral Dissertation.
Thesis
The dry reforming reaction of methane (DRR) is one of the solutions utilized to deal with the global warming via the catalyzed reaction of the main greenhouse gas: carbon dioxide (COv2) with methane (CHv4), to produce the syngas of carbon monoxide (CO) and hydrogen (Hv2). Although it is a promising process, catalyst deactivation via coking shortens the life of catalysts and increases the cost of catalyst regeneration/replacement, both of which are important concerns. Hence, the search for catalysts of high activity and coke-resistance is the main goal. In this work, we feature a two-step procedure comprising the analysis and design of active and coke-resistant Ni-based DRR catalysts by employing computational techniques. These techniques include density functional theory (DFT) coupled to the ratings concept developed as a catalysts screening tool. The approach aims to investigate reaction and coking schemes prior to the setup of design criteria for such catalysts. The ratings concept is introduced as a screening tool to identify active and stable DRR catalysts via the interpretation of stability and reactivity ratings (RT-S and RT-R). The concept was then extended for practical applications, where reliable predictions of coke formation and removal rates are demonstrated. Such predictions emerge from the interpretation of experimental apparent activation energy values of Pt and Rh supported catalysts. The predicted trend of coking agrees well with the trend of coke deposition measured via temperature-programmed hydrogenation and temperature-programmed oxidation of these catalysts. Furthermore, optimal operating conditions are determined. Four strategies are proposed based on four types of DRR catalysts. In addition, the surface transformation entailing the interchange between Ni metallic, oxide and carbide during the DRR is studied since the control over these transformations is proposed to be the key factor for tuning the performance of DRR catalysts. Ternary contour plots are used for determining reactive and coke-resistant surface compositions. It is concluded that the surface composition for coke-resistant Ni-based DRR catalysts should consist of less than 10 % carbide and at least 75 % metallic. Finally, the design procedure and criteria for high performance DRR catalysts are discussed, where the control synthesis towards the Ni(111) as the dominant surface together with the control of surface transformation from metallic to carbide is proposed to be the main key.
